Apart from the previously suggested ancestral north and south Indians, Austro-Asiatic and Tibeto-Burman ancestries also played an important role

Levels of admixtures suddenly dropped around 1,600 years ago corresponding with the reign of the Guptas, whose ruling Hindu elite enforced and advocated Vedic Brahminism, as anything that affects the structure of marriages has impact on the genetic structures of populations. Photo: Reuters

New Delhi: A new study reveals that the current population of mainland India descended from four major ancestries, belying previous findings that traced the roots to two known groups.

The study also looks at how socio-cultural norms such as the caste system transformed the genetic structure of Indians.

Researchers have previously suggested that mainland India’s current population largely descended from ancestral north and south Indians. But the authors of the study published on Tuesday say that in addition, Austro-Asiatic and Tibeto-Burman ancestries played an important role. Unlike mainland Indians, the hunter-gatherers of the Andaman archipelago likely share ancestry with present-day Pacific Islanders, representing a fifth ancestry in India.

Partha Majumder, director of the National Institute of Biomedical Genomics (NIBG), and colleagues analyzed genome-wide variations from 367 unrelated Indians belonging to 20 ethnic groups, including two tribal groups from the Andaman and Nicobar Islands, and data from the Human Genome Diversity Panel, a repository of genomic data.

“One of the main questions that we asked was how many ancestral lineages there are that comprises people of India. In India there are essentially four language groups , but these (were) almost completely overlapped by geography,” said Majumdar.

The study looks at how gene exchange and mixing were common among ancestral groups until 1,575 years or 70 generations ago when strict endogamy came into place. The timing corresponds with the reign of the Guptas, whose ruling Hindu elite enforced and advocated Vedic Brahminism, the study said.

“Using genetics, one can find certain kinds of social stories and events that have taken place in the past. The promulgation of social norms led to the genetic structure becoming more rigid. Of course, anything that affects the structure of marriages has impact on the genetic structures of populations. We found that levels of admixtures suddenly dropped around 1,600 years ago,” Majumdar said in a phone interview.

The study said that this estimated time coincides with the historical period of formulation and adoption of socio-cultural norms restricting inter-marriage in large social strata. According to the authors, the current study includes a more geographically and culturally representative sample to furnish an overall view of India’s current genomic diversity and of the peopling of the subcontinent

The study was published in the peer-reviewed journal Proceedings of National Academy of Sciences on Monday.